Optimization of Technological Conditions for Mulberry-black-tea Fermentation and Kinetic Analysis of the Active Ingredients

YANG Qing1 XU Li2 WANG Jun3 PANG Xiao-Li1 SUN Guo-Xia3 WANG Meng3 ZHANG Jin-Liang3 WU Tao4 LIANG Yao3 WU Fu-An3,4(1College of Food Science,Southwest University,Chongqing 400715,China;2College of Biotechnology,Southwest University,Chongqing 400715,China;3College of Biological and Environmental Engineering,Jiangsu University of Science and Technology,Zhenjiang Jiangsu 212018,China;4The Sericultural Research Institute,Chinese Academy of Agricultural Sciences,Zhenjiang Jiangsu 212018,China)

Mulberry-black-tea;Fermentation technological conditions;Single-factor test;Orthogonal test;Active ingredient;Kinetics

Mulberry-black-tea was prepared by following the processing method for making ordinary black tea.Based on single-factor tests,factors including mulberry leaf maturity,fermentation temperature,fermention time and fermentation humidity were investigated to explore their influence on mulberry-black-tea fermentation and to determine ranges of these factors for further optimization.Subsequently,the latter 3 factors were selected to run the orthogonal test with three factors and three levels to obtain the best fermentation technological parameters.The results showed that factors affecting mulberry-black-tea fermentation were in the order of fermentation temperature,fermentation time,and fermentation humidity.The optimum process conditions were fermentation temperature of 20 ℃,fermentation time of 3 h,and relative humidity of 90% when the 2nd to 3rd fresh mulberry leaves below the top buds were used as the raw material.Under these optimum conditions,the prepared mulberry-black-tea was in black bloom and glow,and had a pleasant sweet aftertaste,showing the best comprehensive quality.Kinetic analysis of active ingredient contents in the fermentation process revealed that,as the fermentation time was prolonged,contents of free amino acids and 1-deoxynojirimycin(DNJ)were increased gradually while those of total flavonoids and polyphenolic compounds were reduced gradually.Moreover,the compatibility of various ingredients became more favorable.